泾渭分明（涇渭分明）　

◎ 泾渭分明 jīngwèi-fēnmíng

[as different as the waters of the Jinghe and the Weihe] 泾、渭二水,一清一浊,虽合流汇聚,却清浊分明。比喻是非明了,境界清楚